A conventional inkjet printing system includes a printhead, an ink supply which supplies liquid ink to the printhead, and an electronic controller which controls the printhead. The printhead ejects ink drops through a plurality of orifices or nozzles and toward a print medium, such as a sheet of paper, so as to print onto the print medium. Typically, the orifices are arranged in one or more arrays such that properly sequenced ejection of ink from the orifices causes characters or other images to be printed upon the print medium as the printhead and the print medium are moved relative to each other.
Typically, the printhead ejects the ink drops through the nozzles by rapidly heating a small volume of ink located in vaporization chambers with small electric heaters, such as thin film resisters. Heating the ink causes the ink to vaporize and be ejected from the nozzles. Typically, for one dot of ink, a remote printhead controller typically located as part of the processing electronics of a printer, controls activation of an electrical current from a power supply external to the printhead. The electrical current is passed through a selected thin film resister to heat the ink in a corresponding selected vaporization chamber. The thin film resistors are herein also referred to as firing resistors. A drop generator is herein referred to include a nozzle, a vaporization chamber, and a firing resistor.
Inkjet printhead evolution has increased the number of drop generators per printhead resulting in an improved printhead drop generation rate. The increase in the number of drop generators per printhead has resulted in a corresponding increase in the number of input pads required on a printhead die to energize the corresponding increase in number of firing resistors. One previous type of printhead has 50 drop generators and 50 power input pads to provide power to separate leads each energizing one of the corresponding firing resistors. This type of printhead, however, is impractical to implement above approximately 50 drop generators.
The required number of input pads is significantly reduced in another conventional type of printhead having switching devices, such as field effect transistors (FETs), coupled to each firing resistor to control the application of the electrical current through the selected firing resistors. In one printhead arrangement, the firing resistors are grouped together into primitives, with a single power lead providing power to the source or drain of each corresponding FET for each firing resistor in a primitive. Each FET in a primitive has a separately energizable address lead coupled to its gate, with each address lead shared by multiple primitives. In a typical printing operation, the address leads are controlled so that only a single firing resistor in a primitive is activated at a given time.
In one arrangement, the address lead coupled to the gate of each FET is controlled by a combination of nozzle data, nozzle addresses, and a fire pulse. The nozzle data is typically provided by the electronic controller of the printer and represents the actual data to be printed. The fire pulse controls the timing of the activation of the electrical current through the selected firing resistor. Typical conventional inkjet printing systems employ the electronic controller to control the timing related to the fire pulse. The nozzle address is cycled through all nozzle addresses to control the nozzle firing order so that all nozzles can be fired, but only a single nozzle in a primitive is fired at a given time.
The number of primitives defines the number of drop generators which can be fired at a given time. The number of address leads per primitive defines the number of firing cycles required to fire all drop generators in the printhead. If there are N primitive leads and M address leads, the N primitive leads and M address leads plus a ground lead can service N×M firing resistors. The total number of input leads (i.e., N+M) is minimized when N=M. The ratio of N/M is herein referred to as the primitive to address ratio of the printhead.
One type of printhead, such as described in the above-incorporated Patent Application entitled “A HIGH PERFORMANCE PRINTING SYSTEM AND PROTOCOL,” employs integrated de-multiplexing electronics to receive and process serial print data. In such a printhead, the serial print data is transmitted to the printhead over a high speed serial interface. A serial shift register in the printhead converts serial, multiplexed print data into parallel print data for a firing array of drop generators (i.e., the serial shift register performs a first level of de-multiplexing). The serial shift register provides parallel data to data latches which hold the parallel data constant throughout the firing period for each address selection. In this manner, while one column of nozzles is firing, the shift register is free to bring in print data for the next nozzle column. This type of printhead can include a second level of de-multiplexing which combines the data from the data latches with the address lines to control the gates of corresponding FETs coupled to corresponding firing resistors to control the application of the electrical current through the selected firing resistors. In this arrangement, the FET is capable of switching high firing current directly on the printhead which eliminates the need and expense for external power switching required when a data line is connected directly to the firing resistor and strobbed externally. As the firing frequency and the number of nozzles increase in this type of printhead, the serial channel data rate and/or the number of data input lines must also increase.
With the primitive to address ratio equal to approximately one, printheads typically function satisfactory when the total drop generator count is not very high (e.g., below approximately 400 drop generators per color of ink) and the firing frequency is not very high (e.g., substantially less than 18 Khz). However, with the firing frequency of a printhead very high (e.g., above approximately 18 Khz), the number of address leads is typically limited to a maximum number (e.g., approximately 10 to 15 address leads), because the higher firing rate limits the number of address strobes (i.e., nozzle firings) which can fit within the shortened firing cycle. With an example primitive to address ratio equal to one, the limitation of 10 to 15 address leads correspondingly results in printheads with only approximately 100 to 225 drop generators.
For reasons stated above and for other reasons presented in greater detail in the Description of the Preferred Embodiments section of the present specification, an inkjet printhead is desired which has a relatively very high number of drop generators (e.g., 1000 or more drop generators) that operate at very high frequencies (e.g., frequencies above 18 Khz).